beneath the table to the abstract. Use the Word Count cmd under Utilites menu for counting Significance Heterosexual transmission is the most common mode of HIV infection worldwide. A better understanding of the major viral genotypes involved in mucosal transmission is important for the development of globally effective vaccines to control HIV infection in humans. To design appropriately targeted vaccines, it is important to know whether some HIV variants are preferentially transmitted by heterosexual contact. Objectives To determine whether some variants of simian immunodeficiency virus (SIV) are preferentially transmitted by intravaginal inoculation of adult rhesus macaques. Results Ten adult rhesus macaques were infected with SIVmac251, a pathogenic SIV isolate comprised of a diverse population of viral variants, or quasispecies. Five monkeys were inoculated intravenously and five monkeys were inoculated intravaginally. Blood samples were collected from each animal at weeks 1, 2, 4, 6, and 8, post inoculation, and plasma RNA was extracted for subsequent analysis using the heteroduplex mobility assay (HMA). A segment of the SIV envelope gene spanning the V1-V2 immunodominant region was analyzed. Analysis of variant viral populations indicated that multiple SIV variants established infection in both intravenously and intravaginally inoculated monkeys. In addition, patterns of SIV variants differed among the intravaginally inoculated animals, and in some animals were similar to the pattern of SIV variants observed in the intravenously inoculated monkeys. The lack of a consistent pattern of viral variants among animals intravaginally inoculated with th e same SIVmac251 stock suggests that specific HIV viral variants are not likely to be transmitted preferentially by heterosexual contact. Future Directions HMA analysis will be used to compare the patterns of variation in different regions of the SIV genome (e.g. core or regulatory proteins) among viruses that are transmitted to rhesus macaques after intravenous inoculation and intravaginal inoculation. KEY WORDS intravaginal SIV transmission, heterosexual HIV transmission, viral variants FUNDING NIH Grant RR00169